1. Field of the Invention
The present invention relates to sensor units and, more specifically, to a sensor unit including sensors required for autonomous navigation of a mobile unit.
2. Description of the Background Art
A navigation system is a system which is mounted on a mobile unit, such as a vehicle, and is equipped with a locating unit for identifying the current position of the mobile unit. Specifically, the locating unit receives, via an antenna unit, a high-frequency signal from a positioning system, such as the Global Positioning System (GPS), while the mobile unit is moving within an area where such a high-frequency signal can be received. With the use of the received high-frequency signal, the locating unit derives the current position of the mobile unit. While the mobile unit is moving within an area where a high-frequency signal cannot be received, such as a road in a tunnel, the locating unit uses signals output from an autonomous navigation sensor, typified by a combination of an acceleration sensor and a gyro sensor, to derive the current position of the mobile unit.
FIG. 5 is a block diagram illustrating the configuration of a conventional navigation system. FIG. 6A is an external perspective view of the navigation system illustrated in FIG. 5. FIG. 6B is an internal perspective view of a sensor unit 80 illustrated in FIG. 6A. In FIGS. 5, 6A, and 6B, the navigation system includes an antenna unit 70, the sensor unit 80, and a locating unit 90.
The antenna unit 70 has a rectangular parallelepiped shape having a width of L1, a length of L2, and a height of t1 (refer to FIG. 6A), and is connected to the locating unit 90 via a first signal cable 71. Here, by way of example only, L1 and L2 are approximately 30 mm each, and t1 is approximately 10 mm. The antenna unit 70 accommodates an antenna element 72 and a low noise amplifier (LNA) 73. As for the antenna unit 70, various structures have been suggested (for example, refer to Japanese Patent Laid-Open Publication No. 1992-326202).
The antenna element 72 receives a high-frequency signal from a positioning system for output to the LNA 73. The LNA 73 amplifies the received high-frequency signal, and sends the amplified signal to the first signal cable 71. Such an output high-frequency signal is transmitted via the first signal cable 71 to the locating unit 90.
The sensor unit 80 has a rectangular parallelepiped shape having a width of L3, a length of L4, and a height of t2 (refer to FIG. 6A), and is connected to the locating unit 90 via a second signal cable 81. Here, by way of example only, L3 and L4 are approximately 60 mm each, and t2 is approximately 35 mm. The sensor unit 80 accommodates at least, as an autonomous navigation sensor, a gyro sensor 82 and an acceleration sensor 83 (refer to FIG. 5 and FIG. 6B). The gyro sensor 82 detects an angular velocity around a first axis (that is, Z axis), and transmits an angular velocity signal to the locating unit 90 via the second signal cable 81. The acceleration sensor 83 detects accelerations along second and third axes (that is, X and Y axes), and transmits an acceleration signal indicative of the detected accelerations to the locating unit 90 via the second signal cable 81.
The locating unit 90 includes at least a receiver 91 and a CPU (Central Processing Unit) 92. The receiver 91 receives a signal transmitted through the first signal cable 71. With the use of the received signal, the receiver 91 derives the current position of the mobile unit for output to the CPU 92. The CPU 92 uses the angular velocity signal and the acceleration signal transmitted via the second signal cable 81 to derive the current position of the mobile unit. Also, the CPU 92 uses the current position received from the receiver 91 and/or the current position derived by itself to perform a process required for navigation of the mobile unit.
In the above-described navigation system, however, the locating unit 90 has connected thereto the antenna unit 70 via the first signal cable 71 and the sensor unit 80 via the second signal cable 81. This configuration disadvantageously increases the volume of the navigation system, and also complicates installation or electric wiring of the navigation system.